Method for heating steel plate and method for manufacturing hot-pressed product

ABSTRACT

A steel plate to be heated is a blank having a first region and a second region adjacent to the first region. The blank is heated by direct resistance heating. A jet of cooling medium is applied to the first region during the direct resistance heating such that a temperature of the first region is kept lower than a quenching region while heating the second region to be equal to or higher than the quenching temperature. To provide a clear boundary between the first and second regions, the jet of cooling medium is applied along a slant direction such that the cooling medium expands along the boundary between the first and second regions. Alternatively, a partition member is provided along the boundary between the first and second regions. The heated blank is then press-formed and cooled in a press die to obtain a hot-pressed product.

TECHNICAL FIELD

The present invention relates to a method for heating a steel plate anda method for manufacturing a hot-pressed product.

BACKGROUND ART

Hot-pressed products are used in, for example vehicles such asautomobiles, from the viewpoints of increase in strength and weightreduction. Hot-pressed products are obtained by hot-pressing a sheet ofsteel blank and quenching it by cooling it under a pressed conditiontogether with a pressing die. The blank is heated by, for example,direct resistance heating in which electric current passed through theblank.

Hot-pressed products may be formed to partially have one or moreunquenched regions. Unquenched regions are subjected to post-processingsuch as piercing, trimming, or welding. According to a related art, ajet of cooling gas is applied to a selected region of a blank during thedirect resistance heating, so that the temperature of the selectedregion is kept lower than a quenching temperature (see, e.g., U.S. Pat.No. 6,903,296B2).

In this related art, the jet of cooling gas is applied to both sides ofthe selected region perpendicularly and at a central part of theselected region. The jet of cooling gas applied to the selected regionin this manner is dispersed around the selected region along the frontsurface and the back surface, suppressing the temperature increase alsoin the area around the selected region. With the rapid cooling of theblank after the heating, the blank is not quenched in the selectedregion in which the temperature is kept lower than the quenchingtemperature, whereas the blank is quenched in the area around theselected region where the temperature is increased to be equal to orhigher than the quenching temperature. However, a desired hardnessdistribution may not be obtained sometimes, due to an expansion of atransition area between the unquenched region and the quenched regionresulting from the suppression of the temperature increase in the areaaround the selected region.

SUMMARY

Illustrative aspects of the present invention provide a method forheating a steel plate with a clear boundary between a region where thetemperature is increased to be equal to or higher than a quenchingtemperature and a region where the temperature is kept lower than thequenching temperature, and also provide a method for manufacturing ahot-pressed product with a clear boundary between a quenched region andan unquenched region.

According to an illustrative aspect of the present invention, a methodfor heating a steel plate is provided. The steel plate is a blank havinga first region and a second region adjacent to the first region. Themethod includes heating the blank by direct resistance heating, andapplying a jet of cooling medium to the first region on at least one ofa front surface and a back surface of the blank during the directresistance heating such that a temperature of the first region is keptlower than a quenching region while heating the second region to beequal to or higher than the quenching temperature. The jet of coolingmedium is applied along a slant direction that is inclined toward thesecond region from a direction perpendicular to the at least one of thefront surface and the back surface in the first region such that the jetof cooling medium expands along a boundary between the first region andthe second region.

According to another illustrative aspect of the present invention,another method for heating the steel plate is provided. The methodincludes heating the blank by direct resistance heating, and applying ajet of cooling medium to the first region on at least one of a frontsurface and a back surface of the blank during the direct resistanceheating such that a temperature of the first region is kept lower than aquenching region while heating the second region to be equal to orhigher than the quenching temperature. A partition member is provided toextend along the boundary between the first region and the second regionon the at least one of the front surface and the back surface of theblank.

According to another illustrative aspect of the present invention, amethod for manufacturing a hot-pressed product is provided. The methodincludes heating the blank by one of the methods described above,press-forming the heated blank by a press die, and cooling the blankinside the press die to quench the second region.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a plan view of an example of a blank, illustrating an exampleof its heating pattern.

FIG. 2 illustrates a method for heating the blank with the heatingpattern illustrated in FIG. 1.

FIG. 3 illustrates the heating method together with FIG. 2.

FIG. 4 is a graph illustrating an example of temperature variations infirst and second regions of the blank when it is heated by the heatingmethod illustrated in FIGS. 2 and 3.

FIG. 5 illustrates a modification of the heating method illustrated inFIGS. 2 and 3.

FIG. 6 is a plan view of another example of a heating pattern of theblank.

FIG. 7 illustrates a method for heating the blank with the heatingpattern illustrated in FIG. 6.

FIG. 8 illustrates the heating method together with FIG. 7.

FIG. 9 illustrates an example of a method for manufacturing ahot-pressed product, according to an embodiment of the presentinvention.

FIG. 10 is a plan view of another example of a blank and its heatingpattern.

FIG. 11A illustrates a method for heating the blank with the heatingpattern illustrated in FIG. 10.

FIG. 11B illustrates the heating method together with FIG. 11A.

FIG. 11C illustrates the heating method together with FIGS. 11A and 11B.

FIG. 12A illustrates the heating method together with FIGS. 11A to 11C.

FIG. 12B illustrates the heating method together with FIGS. 11A to 12A.

FIG. 12C illustrates the heating method together with FIGS. 11A to 12B.

FIG. 13 is a diagram illustrating a control of a movement speed of afirst electrode and an amount of electric current when heating the blankto be in a prescribed temperature range with the method illustrated inFIGS. 11A to 12C.

FIG. 14 is a graph showing an example of the control of the movementspeed of the first electrode and the amount of electric current in themethod illustrated in FIGS. 11A to 12C.

FIG. 15 is a graph showing another example of the control of themovement speed of the first electrode and the amount of electric currentin the method illustrated in FIGS. 11A to 12C.

FIG. 16 is a plan view illustrating another example of a heating patternof the blank.

FIG. 17A illustrates a method for heating the blank with the heatingpattern illustrated in FIG. 16.

FIG. 17B illustrates the heating method together with FIG. 17A.

FIG. 17C illustrates the heating method together with FIGS. 17A and 17B.

FIG. 18A illustrates the heating method together with FIGS. 17A to 17C.

FIG. 18B illustrates the heating method together with FIGS. 17A to 18A.

FIG. 18C illustrates the heating method together with FIGS. 17A to 18B.

FIG. 19 illustrates another method for heating the blank with theheating pattern illustrated in FIG. 1.

FIG. 20 illustrates the heating method together with FIG. 19.

FIG. 21 illustrates a modification of the heating method illustrated inFIGS. 19 and 20.

FIG. 22 illustrates another method for heating the blank with theheating pattern illustrated in FIG. 6.

FIG. 23 illustrates the heating method together with FIG. 22.

FIG. 24A illustrates another method for heating the blank with theheating pattern illustrated in FIG. 10.

FIG. 24B illustrates the heating method together with FIG. 24A.

FIG. 24C illustrates the heating method together with FIGS. 24A and 24B.

FIG. 25A illustrates the heating method together with FIGS. 24A to 24C.

FIG. 25B illustrates the heating method together with FIGS. 24A to 25A.

FIG. 25C illustrates the heating method together with FIGS. 24A to 25B.

FIG. 26A illustrates a method for heating the blank with the heatingpattern illustrated in FIG. 16.

FIG. 26B illustrates the heating method together with FIG. 26A.

FIG. 26C illustrates the heating method together with FIGS. 26A and 26B.

FIG. 27A illustrates the heating method together with FIGS. 26A to 26C.

FIG. 27B illustrates the heating method together with FIGS. 26A to 27A.

FIG. 27C illustrates the heating method together with FIGS. 26A to 27B.

DESCRIPTION OF EMBODIMENTS

FIG. 1 illustrates an example of a blank 1 and its heating pattern.

The blank 1 illustrated in FIG. 1 is a rectangular steel plate having aconstant (including substantially constant) sectional area along thelongitudinal direction of the blank 1. The blank 1 is for manufacture ofa hot-pressed product and is to be subjected to quenching.

The heating pattern of the blank 1 illustrated in FIG. 1 has two firstregions A1 which are side areas located on the two respective sides inthe width direction and extending in the longitudinal directionexcluding both end regions in the longitudinal direction and a secondregion B1 which is a central area between the two first regions A1. Theblank 1 is to be heated so that its temperature is increased to an Ac3transformation point or higher in the second region B1 while being keptlower than an Ac1 transformation point in the first regions A1.

The Ac1 transformation point is a temperature at which ferrite andpearlite of steel of which the blank 1 is made start to undergotransformation to austenite, and the Ac3 transformation point is atemperature at which ferrite and pearlite of the steel of which theblank 1 is made complete the transformation to austenite.

FIGS. 2 and 3 illustrate a method for heating the blank 1 with theheating pattern illustrated in FIG. 1.

Electrodes 2 are fixed at respective longitudinal ends of the blank 1,and the blank 1 is heated as electric current is passed through theblank 1 in its longitudinal direction between the two electrodes 2.During the direct resistance heating, a jet of cooling medium is appliedto at least one of the front surface and the back surface of each of thefirst regions A1. As a result, the temperature of the blank 1 isincreased to be equal to or higher than the Ac3 transformation point inthe second region B1 while being kept lower than the Ac1 transformationpoint in the first regions A1.

In the example illustrated in FIGS. 2 and 3, coolant dischargers 3, eachconfigured to discharge the cooling medium, are disposed on a side ofthe front surface of the blank 1 and the jet of cooling medium isapplied only to the front surfaces of the first regions A1.Alternatively, the coolant dischargers 3 may be disposed on a side ofthe back surface of the blank 1 so that the jet of cooling medium isapplied only at the back surfaces of the first regions A1. As a furtheralternative, the coolant dischargers 3 may be disposed on both sides ofthe blank 1 so that the jet of cooling medium is applied to the frontand back surfaces of the first regions A1. The cooling medium is notparticularly limited. The cooling medium is, for example, air.

Each coolant discharger 3 extends along the associated side edge of theblank 1 and has a plurality of nozzles 4 arranged at intervals in theextending direction of the coolant discharger 3. The center axis of eachnozzle 4 is inclined toward the second region B1 from the directionperpendicular to the front surface of the first region A1. The coolingmedium emitted from the nozzles 4 is directed in the slant directionthat is inclined toward the second region B1 from the directionperpendicular to the front surface of the first region A1, and isapplied to the front surface of the first region A1 such that a jet ofcooling medium expands in a form of a curtain along the boundary betweenthe first region A1 and the second region B1. Instead of the nozzles 4,the coolant discharger 3 may have one or more slits extending in theextending direction of the coolant discharger 3. The nozzles 4 or theslits may be arranged in a plurality of rows.

The jet of cooling medium applied to the front surface of the firstregion A1 flows along the front surface of the first region A1. Beingdirected in the slant direction that is inclined toward the secondregion B1 from the direction perpendicular to the front surface of thefirst region A1, the cooling medium flows off the edge of the blank 1 inthe width direction. In other words, the cooling medium is preventedfrom flowing into the second region B1 from the first region A1. Thus,an area C1 of the second region B1 adjoining the first region A1 isprevented from being cooled by the cooling medium so that the entiresecond region B1, including the area C1, can be heated to be equal to orhigher than the Ac3 transformation point. As a result, clear boundariescan be formed between the second region B1 where the blank 1 is heatedto be equal to or higher than the Ac3 transformation point and the firstregions A1 where the temperature of the blank 1 is kept lower than theAc1 transformation point.

FIG. 4 illustrates an example of temperature variations in the firstregions A1 and the second region B1 of the blank 1 when it is heated bythe heating method illustrated in FIGS. 2 and 3.

In the example illustrated in FIG. 4, direct resistance heating of theblank 1 is started at t₀, application of a jet of cooling medium to thefirst region A1 of the blank 1 is started at t₁, after a given period oftime from to, and the direct resistance heating of the blank 1 isfinished at t₂.

The temperatures in the first regions A1 and the second region B1increase approximately in the same manner from the start of directresistance heating (t₀) to the start of application of the coolingmedium (t₁). A temperature T₁ in the first regions A1 and the secondregion B1 at the start of application of the cooling medium is higherthan room temperature and lower than the Ac1 transformation point.

In the interval between the time of the start of the application of thecooling medium (t₁) and the time of the end of the direct resistanceheating (t₂), the portions of the blank 1 in the first regions A1 arecooled by the cooling medium and the temperature in the first regions A1is not increased from the temperature T₁ at the start of the applicationof the cooling medium, that is, is kept lower than the Ac1transformation point. On the other hand, the temperature in the secondregion B1 continues to increase and becomes higher than the Ac3transformation point at the end of the direct resistance heating (t₂).

Although the application of the cooling medium may be started at thesame time as the start of the direct resistance heating, the differencebetween the temperature in the first regions A1 and the temperature inthe second region B1 in the period from the start of the application ofthe cooling medium to the end of the direct resistance heating can bereduced by starting the application of the cooling medium after a givenperiod of time from the start of the direct resistance heating. As aresult, heat transfer from the second region B1 to the first regions A1can be suppressed and clearer boundaries can be formed between them.

Since resistivity depends on temperature, the resistivity of the blank 1in the first regions A1 where the temperature is relatively low issmaller than in the second region B1 where the temperature is relativelyhigh. Thus, a relatively large current tends to flow through theconduction path extending along the first region A, that is, in thelongitudinal direction of the blank 1. But this current difference ismade smaller by reduction of the difference between the temperature inthe first regions A1 and the temperature in the second region B1. Thisserves to suppress overheating in areas D1 (see FIG. 2) that are locatedin the second region B1 and adjoining the first regions A1 in thecurrent flow direction.

From the viewpoints of suppressing the heat transfer from the secondregion B1 to the first regions A1 and the overheating in the areas D1adjoining the first regions A1 in the current flow direction, it ispreferable to keep the temperature in the first regions A1 between 300°C. and 700° C. in the period from the start of application of thecooling medium to the end of the direct resistance heating. Thetemperature in the first regions A1 can be adjusted as appropriate bycontrolling, for example, the temperature of the cooling medium, theflow rate of the cooling medium, and/or discharging method (e.g.,continuous or intermittent) of the cooling medium.

FIG. 5 illustrates a modification of the heating method illustrated inFIGS. 2 and 3.

In the heating method illustrated in FIGS. 2 and 3, the blank 1 issupported in such a manner that its two end portions in the longitudinaldirection are held by the respective electrodes 2. In this case, theblank 1 may be bent, for example, due to its thermal expansion in thelongitudinal direction caused by the direct resistance heating orpressure produced by receiving the jet of cooling medium. If the blank 1is bent, the relative positions of the first regions A1 of the blank 1and the respective coolant dischargers are changed, so that theapplication of the cooling medium onto the first regions A1 of the blank1 becomes less effective.

In view of the above, in the example illustrated in FIG. 5, the jet ofcooling medium is applied to the front surfaces of the first regions A1in a state in which the back surfaces, opposite to the front surfaces,of the first regions A1 are supported by support members 5. With thisconfiguration, the bend of the blank 1 is suppressed, whereby the jet ofcooling medium can be applied to the first regions A1 in a desiredmanner and hence clearer boundaries can be formed between the secondregion B1 and the first regions A1.

Either of the front surface and the back surface of the blank 1 or bothof the front surface and the back surface of the blank 1 may besupported by support members 5 as appropriate so as to attain thepurpose of suppressing the bend of the blank 1, irrespective of whetherthe jet of cooling medium is applied to the front surface and/or theback surface of the blank 1.

It is preferable that the support members 5 be members that support theportions of the blank 1 in the first regions A1 at points, such as pins.This makes it possible to suppress heat transfer from the portions inthe first regions A1 of the blank 1 to the support members 5 and toprevent obstruction of flows of the cooling medium in the case where theblank 1 is supported by support members 5 at the surface to which thejet of cooling medium is applied. To support the portion of the blank 1in each first region A1, one or more support members 5 are providedaccording to the size of the first region A1.

The heating pattern of the blank 1 is not limited to the exampleillustrated in FIG. 1. FIG. 6 illustrates another example of the heatingpattern in which a first region A2 is provided in the middle of theblank 1 as a closed region surrounded by a second region B2. Although inthe example illustrated in FIG. 6 the first region A2 is a circle, theshape of the first region A2 is not limited to it and may be a rectangleor the like. Further, a plurality of first regions A2 may be provided.

FIGS. 7 and 8 illustrate a method for heating the blank 1 with theheating pattern illustrated in FIG. 6.

Electrodes 2 are fixed at respective longitudinal ends of the blank 1,and the blank 1 is heated as electric current is passed through theblank 1 in its the longitudinal direction between the two electrodes 2.During the direct resistance heating, a jet of cooling medium is appliedto the front surface of the first region A2. As a result, thetemperature of the blank 1 is increased to the Ac3 transformation pointor higher in the second region B2 while being kept lower than the Ac1transformation point in the first region A2.

A coolant discharger 13 has an annular configuration. The cooling mediumemitted from the coolant discharger 13 flows in slant directions thatare inclined toward the second region B2 from the directionperpendicular to the front surface of the first region A2, and isapplied to the front surface of the first region A2 a such that a jet ofcooling medium expands in a form of a curtain along the boundary betweenthe first region A2 and the second region B2.

The jet of cooling medium applied to the front surface of the firstregion A21 flows along the front surface of the first region A2. Beingdirected in the slant direction that is inclined toward the secondregion B2 from the direction perpendicular to the front surface of thefirst region A2, the cooling medium flows from the circumference of thefirst region A2 toward its center. In other words, the cooling medium isprevented from flowing into the second region B3 from the first regionA2. Thus, an area C2 of the second region B2 adjoining the first regionA2 is prevented from being cooled by the cooling medium so that theentire second region B2, including the area C2, can be heated to beequal to or higher than the Ac3 transformation point. As a result, aclear boundary can be formed between the second region B2 where theblank 1 is heated to be equal to or higher than the Ac3 transformationpoint and the first region A2 where the temperature of the blank 1 iskept lower than the Ac1 transformation point.

In the heating method illustrated in FIGS. 7 and 8, the cooling mediumis applied only to the front surface of the blank 1. However, thecooling medium may be applied only to the back surface of the blank 1 orboth the front surface and the back surface of the blank 1. Likewise,the blank 1 may be supported only at the front surface of the blank 1,only at the back surface of the blank 1 or both the front surface andthe back surface of the blank 1.

The first regions A1 illustrated in FIG. 1 and the first region A2illustrated in FIG. 6 may be formed in the single blank 1. In this case,the heating method illustrated in FIGS. 2 and 3 and the heating methodillustrated in FIGS. 7 and 8 are performed in parallel.

The blank 1 whose temperature has been kept lower than the Ac1transformation point in the first region A1, A2 and increased to beequal to or higher than the Ac3 transformation point in the secondregion B1, B2 is press-formed by a press die 20 and then cooled insidethe press die 20 (see FIG. 9), so that the second region B1, B2 isquenched. A clear boundary is formed between the first region A1, A2where the temperature has been kept lower than the Ac1 transformationpoint and the second region B1, B2 where the temperature has beenincreased to be equal to or higher than the Ac3 transformation point,that is, a clear boundary is formed between the unquenched region (firstregion) and the quenched region (second region).

A method of heating a steel plate and a method for manufacturing ahot-pressed product have been described so far in connection with therectangular blank 1 having a constant (includes approximately constant)sectional area along the longitudinal direction of the blank 1. However,the blank is not limited to this example. FIG. 10 illustrates anotherblank 101 and an example of its heating pattern.

The blank 101 illustrated in FIG. 10 is a non-rectangular steel platehaving a constant thickness and a gradually decreasing width from oneend R to the other end L along the longitudinal direction of the blank101. Thus, in the blank 101, the area of the cross section takenorthogonally to the longitudinal direction decreases monotonously andhence the resistance per unit length in the longitudinal directionincreases monotonously as the position goes from the relatively wide endR to the relatively narrow end L. The blank 101 is used for manufactureof a hot-pressed product and is subjected to quenching.

The “sectional area increases or decreases monotonously” means that thesectional area increases or decreases as the position comes close to oneend in the longitudinal direction without occurrence of an inflectionpoint. The sectional area can be regarded as increasing or decreasingmonotonously unless a partial low-temperature portion orhigh-temperature portion that would cause a problem in practical useoccurs due to excessive non-uniformity in the current density in thewidth direction during direct resistance heating.

The heating pattern of the blank 101 illustrated in FIG. 10, which issimilar to that of the blank 1 illustrated in FIG. 1, has two firstregions A3 which are side areas located on the two respective sides inthe width direction and extending in the longitudinal directionexcluding both end regions in the longitudinal direction and a secondregion B3 which is a central area between the two first regions A3. Theblank 101 is to be heated so that its temperature is increased to theAc3 transformation point or higher in the second region B3 while beingkept lower than the Ac1 transformation point in the first regions A3.

FIGS. 11A to 12C illustrate a method for heating the blank 101 with theheating pattern illustrated in FIG. 10.

First, as illustrated in FIG. 11A to 11C, a first electrode 102 a and asecond electrode 102 b are placed adjacent to the relatively wide end Rof the blank 101.

Then, as illustrated in FIGS. 12A to 12C, while current is caused toflow through the blank 101 between the first electrode 102 a and thesecond electrode 102 b, the first electrode 102 a is moved toward theend L of the blank 101 and the distance between the first electrode 102a and the second electrode 102 b is thereby increased gradually. Currentflows through the region between the first electrode 102 a and thesecond electrode 102 b and this region is heated. This direct resistanceheating of the blank 101 is finished after the first electrode 102 areaches the end L.

Coolant dischargers 103, each configured to discharge cooling medium,are disposed on the front surface side of the blank 101. As illustratedin FIG. 11B, at a start of direct resistance heating, a space throughwhich the first electrode 102 a can pass exists between the frontsurface of the blank 101 and the coolant dischargers 103. As illustratedin FIG. 12B, after the first electrode 102 a has passed the firstregions A3 of the blank 101, the interval between the front surface ofthe blank 101 and the coolant dischargers 103 is decreased by moving thecoolant dischargers 103 toward the front surface of the blank 101 andthe application of the jet of cooling medium to the front surfaces ofthe first regions A3 is started. As a result, the temperature of theblank 1 is increased to the Ac3 transformation point in the secondregions B3 while being kept lower than the Ac1 transformation point inthe first regions A3.

A description will now be made of a method for heating the blank 101such that the entire blank 101 becomes within a prescribed temperaturerange with a temperature distribution that can be regarded substantiallyuniform, assuming that the cooling medium is not applied to the firstregions A3. As illustrated in FIG. 11A, the blank 101 is divided into nsegments w1, w2, . . . , wn each having a length A1. With Ii (A) beingelectric current that flows when the first electrode 102 a passes an ithsegment wi, and ti (sec) being a time in which the first electrode 102 apasses the ith segment wi, since the ith segment wi is heated after thefirst electrode 102 a has passed the ith segment wi, a temperatureincrease θi of the ith segment wi is given by the following equation,where ρe being the resistivity (Ω·m), ρi being the density (kg/m³), cbeing the specific heat (J/kg·° C.), and Ai being the sectional area(m²) of the ith segment wi.

$\begin{matrix}{\theta_{i} = {\frac{\rho_{e}}{C\; \rho}\frac{1}{A_{t}^{2}}{\underset{i}{\overset{n}{\Sigma}}( {I_{i}^{2} \times t_{i}} )}}} & \lbrack {{Math}.\mspace{11mu} 1} \rbrack\end{matrix}$

The movement speed of the first electrode 102 a and the current flowingthrough the blank 101 are controlled by a control unit (not shown) froma start to an end of current flow through the blank 101. This makes itpossible to control the quantities of heat that are generated in therespective strip-shaped segments w1, w2, . . . , wn which are obtainedby dividing the blank 101 imaginarily in the longitudinal direction.

In particular, where the first electrode 102 a is moved in thelongitudinal direction of the blank 101 and the sectional area of theblank 101 decreases monotonously in the movement direction of the firstelectrode 102 a, it is possible to heat the blank 101 so that the entireblank 101 will be in such a prescribed temperature range that thetemperature distribution can be regarded substantially uniform. FIG. 13is a conceptual diagram for description of how the movement speed of thefirst electrode 102 a and the current to flow through the blank 101should be controlled to heat the blank 101 to within a prescribedtemperature range.

The temperature increase of the ith segment wi of the case that theblank 101 is divided into the n segments w1-wn having the length A1 isgiven by the foregoing equation. The temperature increases θ1-θn of therespective segments w1-wn are made identical (θ1=θ2= . . . =θn) bycontrolling the current Ii and the time ti (electrode movement speed Vi)so that the following equation is satisfied:

$\begin{matrix}{{\frac{1}{A_{1}^{2}}{\underset{i = 1}{\overset{n}{\Sigma}}( {I_{i}^{2} \times t_{i}} )}} = {{\frac{1}{A_{2}^{2}}{\underset{i = 2}{\overset{n}{\Sigma}}( {I_{i}^{2} \times t_{i}} )}} = {\cdots = {\frac{1}{A_{n}^{2}}{\underset{i = n}{\overset{n}{\Sigma}}( {I_{i}^{2} \times t_{i}} )}}}}} & \lbrack {{Math}.\mspace{11mu} 2} \rbrack\end{matrix}$

Where the second electrode 102 b is fixed at the end R of the blank 101and the first electrode 102 a is moved from the end R to the end L ofthe blank 101, the w1-wn are different from each other in energizationtime and the energization time increases as the position comes closer tothe end R. If the same current is caused to flow through segments on theside of the end R and segments on the side of the end L for the sametime, a smaller quantity of heat is generated in the segment that iscloser to the end R (the resistance per unit length decreases). In viewof this, the blank 1 can be heated so as to be in a prescribedtemperature range by adjusting the quantity of heat generated in eachsegment wi by controlling one or both of the movement speed of the firstelectrode 102 a and the current to flow through the blank 101 accordingto the variation of the resistance per unit length.

FIGS. 14 and 15 illustrate examples relationships between the position Xof the first electrode 102 a in the longitudinal direction and thetemperature T of the blank 101 at the end of the direct resistanceheating, the current I flowing through the blank 101, the movement speedV of the first electrode 102 a, and the elapsed time t from the start ofthe direct resistance heating. In FIGS. 14 and 15, the position X of thefirst electrode 102 a is the distance from the origin (close to the endR of the blank 101) that is the initial position of the first electrode102 a at the start of the direct resistance heating.

In the example illustrated in FIG. 14, adjustments are made so that thefirst electrode 102 a is moved at a constant speed from the end R to theend L of the blank 101 and the current flowing through the blank 101decreases gradually. For a prescribed time after arrival of the firstelectrode 102 a at the end L, the first electrode 102 a is held at theend L and the flow of the same current as at the time of the arrival ofthe first electrode 102 a at the end L is continued. With this currentadjustment, the blank 1 can be heated so as to be in a prescribedtemperature range.

In the example illustrated in FIG. 14, adjustments are made so that aconstant current flows through the blank 101 and the first electrode 102a is moved from the end R to the end L of the blank 101 in such a mannerthat its movement speed increases gradually. For a prescribed time afterarrival of the first electrode 102 a at the end L, the first electrode102 a is held at the end L and a constant current is caused to flowthrough the blank 101. With this speed adjustment, the blank 1 can beheated so as to be in a prescribed temperature range.

Again referring to FIGS. 12A to 12C, though it is possible to heat theblank 101 so that the entire blank 101 is in a prescribed temperaturerange that is higher than or equal to the Ac3 transformation point, thetemperature of the portions of the blank 101 in the first regions A3 iskept lower than the Ac1 transformation point by applying the jet ofcooling medium to the front surfaces of the first regions A3. Eachcoolant discharger 103 configured to discharge a jet of cooling mediumextends alongside the associated side edge of the blank 1, and has aplurality of nozzles 104 arranged at intervals in the extendingdirection of the coolant discharger 103. The center axis of each nozzle104 is inclined toward the second region B3 from the directionperpendicular to the front surface of the first region A3. The coolingmedium emitted from the nozzles 104 is directed in the slant directionthat is inclined toward the second region B3 from the directionperpendicular to the front surface of the first region A3, and isapplied to the front surface of the first region A3 such that a jet ofcooling medium expands in a form of a curtain along the boundary betweenthe first region A3 and the second region B3.

The jet of cooling medium applied to the front surface of the firstregion A3 flows along the front surface of the first region A3. Beingdirected in the slant direction that is inclined toward the secondregion B3 from the direction perpendicular to the front surface of thefirst region A3, the cooling medium flows off the edge of the blank 101in the width direction. In other words, the cooling medium is preventedfrom flowing into the second region B3 from the first region A3 to thesecond region B3. Thus, the area C3 of the second region B3 adjoiningthe first region A3 is prevented from being cooled by the cooling mediumso that the entire second region B3, including the area C3, can beheated to be equal to or higher than the Ac3 transformation point. As aresult, clear boundaries can be formed between the second region B3where the blank 101 is heated to be equal to or higher than the Ac3transformation point and the first regions A3 where the temperature ofthe blank 101 is kept lower than the Ac1 transformation point.

FIG. 16 illustrates another example heating pattern of the blank 101.

The heating pattern illustrated in FIG. 16 is similar to the heatingpattern of the blank 1 illustrated in FIG. 6. In this heating pattern, afirst region A4 where the temperature is to be kept lower than the Ac1transformation point is a closed central area surrounded by a secondregion B4 where the temperature is to be increased to the Ac3transformation point or higher.

FIGS. 17A to 18C illustrate a method for heating the blank 101 with theheating pattern illustrated in FIG. 16.

First, as illustrated in FIG. 17A to 17C, a first electrode 102 a and asecond electrode 102 b are placed adjacent to the relatively wide end Rof the blank 101.

Then, as illustrated in FIGS. 18A to 18C, while current is caused toflow through the blank 101 between the first electrode 102 a and thesecond electrode 102 b, the first electrode 102 a is moved toward theend L of the blank 101 and the distance between the first electrode 102a and the second electrode 102 b is thereby increased gradually. Currentflows through the region between the first electrode 102 a and thesecond electrode 102 b and this region is heated. This direct resistanceheating of the blank 101 is finished after the first electrode 102 areaches the end L.

A coolant discharger 113 has an annular configuration. The coolingmedium emitted from the coolant discharger 113 flows in slant directionsthat are inclined toward the second region B4 from the directionperpendicular to the front surface of the first region A4, and isapplied to the front surface of the first region A4 such that a jet ofcooling medium expands in a form of a curtain along the boundary betweenthe first region A4 and the second region B4.

The jet of cooling medium applied to the front surface of the firstregion A4 flows along the front surface of the first region A4. Beingdirected in the slant direction that is inclined toward the secondregion B4 from the direction perpendicular to the front surface of thefirst region A4, the cooling medium flows from the circumference of thefirst region A4 toward its center. In other words, the cooling medium isprevented from flowing into the second region B4 from the first regionA4. Thus, an area C3 of the second region B1 adjoining the first regionA4 is prevented from being cooled by the cooling medium so that theentire second region B4, including the area C4, can be heated to beequal to or higher than the Ac3 transformation point. As a result, aclear boundary can be formed between the second region B4 where theblank 101 is heated to be equal to or higher than the Ac3 transformationpoint and the first region A4 where the temperature of the blank 101 iskept lower than the Ac1 transformation point.

In the heating method illustrated in FIGS. 11A to 11C and 12A to 12C andthe heating method illustrated in FIGS. 17A to 17C and 18A to 18C, thejet of cooling medium may be applied to only the front surface of theblank 101, only the back surface of the blank 101, or both of the frontand back surfaces of the blank 101. Also, the blank 101 may be supportedat only the front surface of the blank 101, the back surface of theblank 101, or both the front and back surfaces of the blank 101.

The first regions A3 illustrated in FIG. 10 and the first region A4illustrated in FIG. 16 may be formed in the single blank 101. In thiscase, the heating method illustrated in FIGS. 11A to 11C and 12A to 12Cand the heating method illustrated in FIGS. 17A to 17C and 18A to 18Care performed in parallel.

The blank 101 described above is constant in thickness and is notrectangular in shape, that is, the width decreases gradually from theend R to the end L in the longitudinal direction. Alternatively, a blankmay be used that is constant in width and whose thickness decreasesgradually from the end R to the end L in the longitudinal direction. Asa further alternative, a non-rectangular blank may be used whosethickness and width decrease gradually from the end R to the end L inthe longitudinal direction.

The blank 101 whose temperature has been kept lower than the Ac1transformation point in the first region A3, A4 and increased to beequal to or higher than the Ac3 transformation point in the secondregion B3, B4 in the above-described manner is press-formed by a pressdie and then cooled inside the press die so that the second region B3,B4 is quenched. A clear boundary is formed between the first region A3,A4 where the temperature has been kept lower than the Ac1 transformationpoint and the second region B3, B4 where the temperature has beenincreased to be equal to or higher than the Ac3 transformation point,that is, a clear boundary is formed between the unquenched region (firstregion) and the quenched region (second region).

FIGS. 19 and 20 illustrate another method for heating the blank 1 withthe heating pattern illustrated in FIG. 1. Features that are differentthan in the heating method illustrated in FIGS. 2 and 3 will bedescribed mainly below. Descriptions of features and advantages that arethe same as or similar to features and advantages of the heating methodillustrated in FIGS. 2 and 3 may not be made when appropriate to avoidredundant descriptions.

In the heating method illustrated in FIGS. 19 and 20, coolantdischargers 123, each configured to discharge cooling medium, andpartition members 6 are disposed on a side of the front surface of theblank 1, and a jet of cooling medium is applied only to the frontsurfaces of the first regions A1. Alternatively, the coolant dischargers3 and the partition members 6 may be disposed on a side of the backsurface of the blank 1 so that the jet of cooling medium is applied onlyto the back surfaces of the first regions A1. As a further alternative,the coolant dischargers 3 and the partition members 6 may be disposed onboth sides of the blank 1 so that the jet of cooling medium is appliedto the front and back surfaces of the first regions A1. The coolingmedium is not particularly limited. The cooling medium is, for example,air.

The partition members 6 extend alongside the respective edges of theblank 1. Each coolant discharger 123 is disposed adjacent to theassociated partition member 6 on the side of the associated first regionA1 so as to extend parallel with the associated partition member 6, andhas a plurality of nozzles 124 arranged at intervals in the extendingdirection of the coolant discharger 123. The cooling medium emitted fromthe nozzles 124 is applied to the front surface of the first region A1such that a jet of cooling medium expands in a form of a curtain alongthe boundary between the first region A1 and the second region B1.Instead of the nozzles 124, the coolant discharger 123 may have one ormore slits extending in the extending direction of the coolantdischarger 123. The nozzles 124 or the slits may be arranged in aplurality of rows.

The jet of cooling medium applied to the front surface of the firstregion A1 flows along the front surface of the first region A1. Thepartition member 6 causes the cooling medium to flow toward the sideopposite to the partition member 6 and off the edge of the blank 1 inthe width direction. In other words, the cooling medium is preventedfrom flowing into the second region B1 from the first region A1. Thus,an areas C1 of the second region B1 adjoining the first region A1 isprevented from being cooled by the cooling medium so that the entiresecond region B1, including the area C1, can be heated to be equal to orhigher than the Ac3 transformation point. As a result, clear boundariescan be formed between the second region B1 where the blank 1 is heatedto be equal to or higher than the Ac3 transformation point and the firstregions A1 where the temperature of the blank 1 is kept lower than theAc1 transformation point. The partition member 6 may be arranged suchthat a slight gap is provided between the partition member 6 and theblank 1. Alternatively, the partition member 6 may be arranged so as tocontact the blank 1, in which case the cooling medium is furtherprevented from flowing into the second region B1 from the first regionA.

For example, temperature variations, in the first regions A1 and thesecond region B1, of the blank 1 when it is heated by the heating methodillustrated in FIGS. 19 and 20 are the same as or similar to the exampletemperature variations, in the first regions A1 and the second regionB1, of the blank 1 (see FIG. 4) when it is heated by the heating methodillustrated in FIGS. 2 and 3.

FIG. 21 is a modification of the heating method illustrated in FIGS. 19and 20.

In the heating method illustrated in FIGS. 19 and 20, the blank 1 issupported in such a manner that its two end portions in the longitudinaldirection are held by the respective electrodes 2. In this case, theblank 1 may be bent, for example, due to its thermal expansion in thelongitudinal direction caused by the direct resistance heating orpressure produced by the application of the jet of cooling medium. Ifthe blank 1 is bent, the positions of the portions of the blank 1 in thefirst regions A1 relative to the respective coolant dischargers arechanged, whereby the application of the cooling medium to the firstregions A1 becomes less effective.

In view of the above, in the example illustrated in FIG. 21, the jet ofcooling medium is applied to the front surfaces of the first regions A1in a state in which the back surfaces, opposite to the front surfaces,of the first regions A1 are supported by support members 5. With thisconfiguration, the bend of the blank 1 is suppressed, whereby the jet ofcooling medium can be applied to the first regions A1 in a desiredmanner and hence clearer boundaries can be formed between the secondregion B1 and the first regions A1. The support members 5 are the sameas or similar to those in the example illustrated in FIG. 5.

FIGS. 22 and 23 illustrate another method for heating the blank 1 withthe heating pattern illustrated in FIG. 6. Features that are differentthan in the heating method illustrated in FIGS. 7 and 8 will bedescribed mainly below. Descriptions of features and advantages that arethe same as or similar to features and advantages of the heating methodillustrated in FIGS. 7 and 8 may not be made when appropriate to avoidredundant descriptions.

A partition member 16 has a cylindrical shape. An inner cylinder 17 isinserted in the partition member 16 approximately coaxially so as to belocated over a central portion of the first region A2. A coolantdischarger 133 which jets out the cooling medium is connected to theinner cylinder 17. The jet of cooling medium emitted from the coolantdischarger 133 is applied to the central portion of the front surface ofthe first region A2. A slight gap may be formed between the partitionmember 16 and the blank 1. However, it is preferable that they be incontact with each other.

The jet of cooling medium applied to the central portion of the frontsurface of the first region A2 flows outward along the front surface ofthe first region A2, hits the partition member 16, and is ejectedthrough the space between the partition member 16 and the inner cylinder17. In other words, the cooling medium is prevented from flowing intothe second region B2 from the first region A2. Thus, an area C2 of thesecond region B2 adjoining the first region A2 is prevented from beingcooled by the cooling medium so that the entire second region B2,including the area C2, can be heated to be equal to or higher than theAc3 transformation point. As a result, a clear boundary can be formedbetween the second region B2 where the blank 1 is heated to be equal toor higher than the Ac3 transformation point and the first region A2where the temperature of the blank 1 is kept lower than the Ac1transformation point.

FIGS. 24A to 25C illustrate another method for heating the blank 101with the heating pattern illustrated in FIG. 10. Features that aredifferent than in the heating method illustrated in FIGS. 11A to 12Cwill be described mainly below. Descriptions of features and advantagesthat are the same as or similar to features and advantages of theheating method illustrated in FIGS. 11A to 12C may not be made whenappropriate to avoid redundant descriptions.

Coolant dischargers 143 and partition members 106 are disposed on thefront surface side of the blank 101. As illustrated in FIGS. 24B and24C, at a start of direct resistance heating, a space through which thefirst electrode 102 a can pass exists between the front surface of theblank 101 and the coolant dischargers 143. As illustrated in FIGS. 25Band 25C, after the first electrode 102 a has passed the first regions A3of the blank 101, the interval between the front surface of the blank101 and the coolant dischargers 143 is decreased by moving the coolantdischargers 143 and the partition members 106 toward the front surfaceof the blank 101 and the application of the jet of cooling medium to thefront surfaces of the first regions A3 is started. As a result, thetemperature of the blank 101 is increased to the Ac3 transformationpoint in the second regions B3 while being kept lower than the Ac1transformation point in the first regions A3.

Though it is possible to heat the blank 101 such that the entire blank101 is in a prescribed temperature range that is equal to or higher thanthe Ac3 transformation point, the temperature of the first regions A3 iskept lower than the Ac1 transformation point by the application of thejet of cooling medium to the front surfaces of the first regions A3. Thepartition members 106 extend alongside the respective edges of the blank101. Each coolant discharger 143 is disposed on the first region A3 sideof the associated partition member 106 so as to extend alongside theassociated partition member 106 and has a plurality of nozzles 144arranged at intervals in the extending direction of the coolantdischarger 143. The cooling medium emitted from the nozzles 144 isapplied to the front surface of the first region A3 such that a jet ofcooling medium expands in a form of a curtain along the boundary betweenthe first region A3 and the second region B3. A slight gap may beprovided between the partition member 106 and the blank 101. However, itis preferable that the partition member 106 and the blank 101 are incontact with each other.

The jet of cooling medium applied to the front surface of the firstregion A3 flows along the front surface of the first region A3. Thepartition member 106 causes the cooling medium to flow toward the sideopposite to the partition member 106 and off the edge the blank 101 inthe width direction. In other words, the cooling medium is preventedfrom flowing in the second region B3 from the first region A3. Thus, anarea C3 inside the second region B3 and adjoining the first region A3 isprevented from being cooled by the cooling medium so that the entiresecond region B3, including the area C3, can be heated to be equal to orhigher than the Ac3 transformation point. As a result, clear boundariescan be formed between the second region B3 where the blank 101 is heatedto be equal to or higher than the Ac3 transformation point and the firstregions A3 where the temperature of the blank 101 is kept lower than theAc1 transformation point.

FIGS. 26A to 27C illustrate another method for heating the blank 101with the heating pattern illustrated in FIG. 16. Features that aredifferent than in the heating method illustrated in FIGS. 17A to 18Cwill be described mainly below. Descriptions of features and advantagesthat are the same as or similar to features and advantages of theheating method illustrated in FIGS. 17A to 18C may not be made whenappropriate to avoid redundant descriptions.

A partition member 116 has a cylindrical shape. An inner cylinder 117 isinserted in the partition member 116 approximately coaxially so as to belocated over a central portion of the first region A4. A coolantdischarger 153 which jets out the cooling medium is connected to theinner cylinder 117. The jet of cooling medium emitted from the coolantdischarger 153 is applied to the central portion of the front surface ofthe first region A4. A slight gap may be formed between the partitionmember 116 and the blank 101. However, it is preferable that they be incontact with each other.

The jet of cooling medium applied to the central portion of the frontsurface of the first region A4 flows outward along the front surface ofthe first region A4, hits the partition member 116, and is ejectedthrough the space between the partition member 116 and the innercylinder 117. In other words, the cooling medium is prevented fromentering into the second region B4 from the first region A4. Thus, anarea C4 of the second region B4 adjoining the first region A4 isprevented from being cooled by the cooling medium so that the entiresecond region B4, including the area C4, can be heated to be equal to orhigher than the Ac3 transformation point. As a result, a clear boundarycan be formed between the second region B4 where the blank 101 is heatedto be equal to or higher than the Ac3 transformation point and the firstregion A4 where the temperature of the blank 101 is kept lower than theAc1 transformation point.

According to one or more illustrative aspects of the embodimentsdescribed above, a method for heating a steel plate is provided. Thesteel plate is a blank having a first region and a second regionadjacent to the first region. The method includes heating the blank bydirect resistance heating, and applying a jet of cooling medium to thefirst region on at least one of a front surface and a back surface ofthe blank during the direct resistance heating such that a temperatureof the first region is kept lower than a quenching region while heatingthe second region to be equal to or higher than the quenchingtemperature. The jet of cooling medium is applied along a slantdirection that is inclined toward the second region from a directionperpendicular to the at least one of the front surface and the backsurface in the first region such that the jet of cooling medium expandsalong a boundary between the first region and the second region, or apartition member is provided to extend along the boundary between thefirst region and the second region on the at least one of the frontsurface and the back surface of the blank.

The jet of cooling medium may be applied along the slant direction suchthat the jet of cooling medium expands in a form of a curtain along theboundary between the first region and the second region. The firstregion may include an edge of the blank, and the jet of cooling mediumapplied to the first region may be caused to flow off the edge of theblank.

The first region may be a closed region surrounded by the second region,and the jet of cooling medium applied to the first region may be causedto flow from a circumference of the first region toward a center of thefirst region.

The partition member may be provided to contact the at least one of thefront surface and the back surface.

When the first region includes an edge of the blank, the partitionmember may extend alongside the edge of the blank to cause the jet ofcooling medium applied to the first region to flow off the edge of theblank.

When the first region is a closed region surrounded by the secondregion, the partition member may have a cylindrical shape to cause thejet of cooling medium applied to the first region to flow from a centerof the first region toward a circumference of the first region.

An inner cylinder may be inserted inside the partition member to applythe jet of cooling medium toward the center of the first region throughthe inner cylinder.

The jet of cooling medium may be applied in a state in which the firstregion is supported on at least one of the front surface and the backsurface to suppress bending of the blank.

The first region may be point-supported at one or more locations on atleast one of the front surface and the back surface.

When the blank is rectangular and has a constant sectional area along alongitudinal direction of the blank, the heating of the blank by thedirect resistance heating may include applying electric current to passthrough the blank via a pair of electrodes fixed at longitudinal ends ofthe blank.

When the blank is non-rectangular and has a sectional area monotonouslydecreasing along a longitudinal direction of the blank from a first endof the blank to a second end of the blank, the heating of the blank bythe direct resistance heating may include placing a pair of electrodeson the first end of the blank, and moving one of the electrodes in thelongitudinal direction toward the second end of the blank while applyingelectric current to pass through a portion of the blank between the pairof electrodes.

The application of the jet of cooling medium to the first region may bestarted after the one of the electrodes has passed the first region.

The temperature of the first region may be kept lower than an Ac1transformation point of the blank while heating the second region to beequal to or higher than an Ac3 transformation point of the blank.

To manufacture a hot-pressed product, the blank heated in a mannerdescribed above is pressed-formed with a press die and cooled inside thepress die to quench the second region.

This application claims priority to Japanese Patent Application Nos.2018-005098 and 2018-005099 both filed on Jan. 16, 2018, the entirecontents of which are incorporated herein by reference.

1. A method for heating a steel plate, the steel plate being a blankhaving a first region and a second region adjacent to the first region,the method comprising: heating the blank by direct resistance heating;and applying a jet of cooling medium to the first region on at least oneof a front surface and a back surface of the blank during the directresistance heating such that a temperature of the first region is keptlower than a quenching region while heating the second region to beequal to or higher than the quenching temperature, wherein the jet ofcooling medium is applied along a slant direction that is inclinedtoward the second region from a direction perpendicular to the at leastone of the front surface and the back surface in the first region suchthat the jet of cooling medium expands along a boundary between thefirst region and the second region; or wherein a partition member isprovided to extend along the boundary between the first region and thesecond region on the at least one of the front surface and the backsurface of the blank.
 2. The method according to claim 1, wherein thejet of cooling medium is applied along the slant direction such that thejet of cooling medium expands in a form of a curtain along the boundarybetween the first region and the second region.
 3. The heating methodaccording to claim 2, wherein the first region includes an edge of theblank, and wherein the jet of cooling medium applied to the first regionis caused to flow off the edge of the blank.
 4. The heating methodaccording to claim 2, wherein the first region is a closed regionsurrounded by the second region, and wherein the jet of cooling mediumapplied to the first region is caused to flow from a circumference ofthe first region toward a center of the first region.
 5. The heatingmethod according to claim 1, wherein the partition member is provided toextend along the boundary between the first region and the second regionon the at least one of the front surface and the back surface of theblank.
 6. The heating method according to claim 5, wherein the partitionmember is provided to contact the at least one of the front surface andthe back surface.
 7. The heating method according to claim 5, whereinthe first region includes an edge of the blank, and wherein thepartition member extends alongside the edge of the blank to cause thejet of cooling medium applied to the first region to flow off the edgeof the blank.
 8. The heating method according to claim 5, wherein thefirst region is a closed region surrounded by the second region, andwherein the partition member has a cylindrical shape to cause the jet ofcooling medium applied to the first region to flow from a center of thefirst region toward a circumference of the first region.
 9. The heatingmethod according to claim 8, wherein an inner cylinder is insertedinside the partition member to apply the jet of cooling medium towardthe center of the first region through the inner cylinder.
 10. Theheating method according to claim 1, wherein the jet of cooling mediumis applied in a state in which the first region is supported on at leastone of the front surface and the back surface to suppress bending of theblank.
 11. The heating method according to claim 10, wherein the firstregion is point-supported at one or more locations on at least one ofthe front surface and the back surface.
 12. The heating method accordingto claim 1, wherein the blank is rectangular and has a constantsectional area along a longitudinal direction of the blank, and whereinthe heating of the blank by the direct resistance heating comprisesapplying electric current to pass through the blank via a pair ofelectrodes fixed at longitudinal ends of the blank.
 13. The heatingmethod according to claim 1, wherein the blank is non-rectangular andhas a sectional area monotonously decreasing along a longitudinaldirection of the blank from a first end of the blank to a second end ofthe blank, and wherein the heating of the blank by the direct resistanceheating comprises: placing a pair of electrodes on the first end of theblank; and moving one of the electrodes in the longitudinal directiontoward the second end of the blank while applying electric current topass through a portion of the blank between the pair of electrodes. 14.The heating method according to claim 13, wherein the application of thejet of cooling medium to the first region is started after the one ofthe electrodes has passed the first region.
 15. The heating methodaccording to claim 1, wherein the temperature of the first region iskept lower than an Ac1 transformation point of the blank while heatingthe second region to be equal to or higher than an Ac3 transformationpoint of the blank.
 16. A method for manufacturing a hot-pressedproduct, the method comprising: heating the blank by the methodaccording to claim 1; press-forming the heated blank by a press die; andcooling the blank inside the press die to quench the second region.